The present invention relates the synthesis of 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole (FFI), and analogs thereof. FFI has been known for a number of years as a fluorescent chromophore formed as a result of the advanced glycosylation process.
The reaction between glucose and proteins has been known for some time. Its earliest manifestation was in the appearance of brown pigments during the cooking of food, which was identified by Maillard in 1912, who observed that glucose or other reducing sugars react with amino acids to form adducts that undergo a series of dehydrations and rearrangements to form stable brown pigments. Maillard, C. R. Acad. Sci., 154, pp. 66-68, (1912). Further studies have suggested that stored and heat treated foods undergo nonenzymatic browning as a result of the reaction between glucose and the polypeptide chain, and that the proteins are resultingly cross-linked and correspondingly exhibit decreased bioavailability.
This reaction between reducing sugars and food proteins was found to have its parallel in vivo. Thus, the nonenzymatic reaction between glucose and the free amino groups on proteins to form a stable, 1-deoxyketosyl adduct, known as the Amadori product, has been shown to occur with hemoglobin, wherein a rearrangement of the amino terminal of the beta-chain of hemoglobin by reaction with glucose, forms the adduct known as hemoglobin A1c. The reaction has also been found to occur with a variety of other body proteins, such as lens crystallins, collagen and nerve proteins. See, for instance, Bucala et al., "Advanced Glycosylation: Chemistry, Biology, and Implications for Diabetes and Aging," in Advances in Pharmacology, Vol. 23, pp. 1-34, Academic Press (1992).
Moreover, brown pigments with spectral and fluorescent properties similar to those of late-stage Maillard products have also been observed in vivo in association with several long-lived proteins, such as lens proteins and collagen from aged individuals. An age-related linear increase in pigment was observed in human dura collagen between the ages of 20 to 90 years. Interestingly, the aging of collagen can be mimicked in vitro by the cross-linking induced by glucose; and the capture of other proteins and the formation of adducts by collagen, also noted, is theorized to occur by a cross-linking reaction, and is believed to account for the observed accumulation of albumin and antibodies in kidney basement membrane.
In Cerami, U.S. Pat. No. 4,665,192, FFI was first identified and characterized. Various utilities for FFI have been proposed, among them, therapeutic methods which utilize FFI as an agent to induce macrophage stimulation, and thus accelerate the body's own process for removal of advanced glycosylation endproducts.
Necessary to such therapeutic methods is a ready and facile process for the chemical synthesis of FFI. Heretofore, preparation was by isolation from natural sources, or via the synthetic route proposed by Chang et al., J. Biol. Chem., 260, pp. 1970-1974 (1985). These methods suffer from poor yields and contaminating by-products which result in the use of difficult purification procedures. The present invention addresses such problems.